1. Technical Field of the Invention
The present invention relates to differential amplifiers and related methods.
2. Description of Related Art
As is known, audio signals are processed by a wide variety of electronic equipment, including portable, or handheld, devices. Such devices include laptop, notebook and other personal computers, personal digital assistants (PDA), CD players, MP3 players, DVD players, AM/FM radios, cellular telephones, etc. Each of these devices includes one or more integrated circuits to provide the functionality of the device. As an example, a computer may include an audio amplifier integrated circuit to support the processing of audio signals in order to produce an audio output that is delivered to the user through speakers, headphones or the like.
One measure of an audio amplifier's performance is total harmonic distortion (THD). When an audio signal is distorted such as by clipping, saturation or other nonlinear effects, undesirable harmonics are generated from each fundamental frequency of the input signal. THD measures the percentage of an output waveform that constitutes these harmonics as a percentage of the total output. It is desirable to design audio amplifiers with small THD in the range of 0.01% or less. This specification can be difficult to maintain for large output voltage swings as the components of the amplifier reach physical device limitations, leave intended operating regions such as regions of linear operation and/or approach the supply voltages that power these devices.
The need exists for audio amplifiers that provide greater output voltage swings while maintaining low THD.